Reservoir wettability can affect reservoir's properties such as, but not limited to, relative permeability, capillary pressure, fluid location, fluid flow, and residual oil distribution. Accurately characterizing reservoir wettability can significantly impact oil production methods and strategy. For example, some Enhanced Oil Recovery (EOR) techniques focus on altering reservoir wettability as a way of recovering more oil. Reservoir wettability can also play an important role in determining whether certain Improved Oil Recovery (IOR) techniques will work in a given reservoir.
As used herein, the term “wettability” refers to the tendency of a particular fluid to spread on or adhere to a solid surface in the presence of another immiscible fluid. As used herein, the term “reservoir wettability” refers to the ability of a reservoir rock surface to preferentially contact a particular fluid.
Wettability of a reservoir rock can be determined by a number of methods using various analytical tools. One method of determining reservoir wettability includes measuring contact angle of an oil droplet on the reservoir rock. Other conventional methods involve measuring work required to do a forced fluid displacement, measuring adsorption of a dye in an aqueous solvent, and following changes in nuclear magnetic resonance (NMR) relaxation times. These wettability studies are typically limited to laboratory experiments involving core samples taken from the reservoir, which may not adequately account for spatial- and production-dependent variations in temperature, pressure, fluid chemistry among other reservoir properties that are found downhole. One of the methods used to characterize wettability of laboratory samples is to measure the rate of spontaneous imbibition of water into an oil-saturated core plug. Imbibition rates are determined from the total oil production from the sample over time. A dimensionless time, which corrects for variations in sample size, pore geometry and certain rock and fluid properties, can provide greater insights into the imbibition processes.